2005 Outback AWD Failure

[Larry Vollintin]

I got stuck recently in the Sierras on a dirt road when I backed over a large angular piece of granite that dropped the right rear wheel into a hole. All the other wheels were firmly on the ground and the chassis did not high center. I thought the AWD in the 5-speed would pull me out with no problem. But all it did was spin the right rear wheel and burn up the clutch. I managed to get out by slipping the jack under the chassis in front of the right rear wheel and jacking up the car enough to put some rocks and large branches under the wheel and the floor matte over the rocks/branches and up the rock, and I finally got out. But I was very disappointed in the car. So, what gives? Thanks. LRV

[subiesailor]

Its a subaru not a 4x4 lol

[plain OM]

It certainly isn't a 4X4 (with locking transfer case and differentials), but if the other three wheels had good traction, the car wasn't on a slope, there was nothing preventing the other wheels from moving, and no part of the body/suspension was on the ground, shouldn't the car have at least appeared to be trying to move (rocking) when the clutch was engaged?

Absolutely no movement would suggest that the center differential's viscous coupler wasn't working, but this is contradicted by the reference to the clutch burning up. If the clutch was overheating, it could only be because there was a significant load on it as it was being engaged, and if that's the case, it could only have come from the front wheels as the rear drive was free to spin (assuming the car does not have a limited slip differential at the rear).

Perhaps I'm misreading the original post . . .

[Larry Vollintin]

I'm the original poster. Every assumption that Plain OM makes is correct. See photo attached (I hope) But checking my original purchase material indicates that the car has "full-time AWD" and a "limited slip rear differential." So, would that explain why no movement with the right rear wheel hanging over the rock? If so, please help a mechanical peasant understand. Also, the left rear wheel was firmly on the ground, but did not move. And, from some Sub website demos and comparisons of variations on AWD, (see Subaru Symmetrical All-Wheel Drive | Subaru AWD, and

Subaru AWD vs. competitors - YouTube

Subaru AWD vs. competitors - YouTube

), it would appear that in my situation, the front wheels (and the other rear wheel) should have pulled me out. So, could center diff or viscous coupling you mention be inoperative? How does one check that? A Sub mechanic recently told me "off the record" that a solution to my predicament would have been to open the fuse box under the hood and to put a fuse into the vacant slot marked "FWD" thereby disabling the AWD and turning the car into just FWD. Then, with no power going to the rear wheels, the front wheels should have been able to pull me out. What do you think of that? I don't really want to repeat the experiment and try the fuse thing, but is this mechanic full of it, or legit? Thanks. LRV

[jp1203]

Originally Posted by Larry Vollintin

I'm the original poster. Every assumption that Plain OM makes is correct. See photo attached (I hope) But checking my original purchase material indicates that the car has "full-time AWD" and a "limited slip rear differential." So, would that explain why no movement with the right rear wheel hanging over the rock? If so, please help a mechanical peasant understand. Also, the left rear wheel was firmly on the ground, but did not move. And, from some Sub website demos and comparisons of variations on AWD, (see Subaru Symmetrical All-Wheel Drive | Subaru AWD, and Subaru AWD vs. competitors - YouTube), it would appear that in my situation, the front wheels (and the other rear wheel) should have pulled me out. So, could center diff or viscous coupling you mention be inoperative? How does one check that? A Sub mechanic recently told me "off the record" that a solution to my predicament would have been to open the fuse box under the hood and to put a fuse into the vacant slot marked "FWD" thereby disabling the AWD and turning the car into just FWD. Then, with no power going to the rear wheels, the front wheels should have been able to pull me out. What do you think of that? I don't really want to repeat the experiment and try the fuse thing, but is this mechanic full of it, or legit? Thanks. LRV
Attachment 24726

That looks like a heck of a ledge to try to pull that wheel out of. It's odd that the front wheels weren't spinning at all (did I read that right?), because one should have been. It sort of looks like even if they were, they would be on loose gravel with most of the weight shifted to the rear (and to one side at that), and I'm not sure you'd have enough traction to get out of that. Hard to tell for sure, though.

[CNY_Dave]

Could be you were just planted so good it was like trying to drive off with the front bumper against a brick wall. In that case you'd just smoke the clutch, too.

[plain OM]

It is indeed quite a ledge to pull the car up and out of, but I would have still expected some movement of the car, sort of a rocking motion, when the clutch was being engaged and the released, or some wheel spin (other than the wheel in the hole) confirming that the other wheels were trying to pull the car forward, but couldn't overcome the ledge.

However, given the apparent drop of the wheel in the photo relative to the wheel well, I wouldn't be surprised if the wheel was hanging freely and some part of the chassis was on the ground. The rear bumper looks as if it might be hung on the slope behind (if not at the right rear corner, then further toward the center), thereby preventing the car from moving backward, and the rocker panel in front of the wheel is pretty low (the "air dam" in front of the wheel is down to the ground), suggesting to me that there could well be a suspension member or the differential support near the center of the car that's on the ground. (It also looks as if it would have been difficult to see if anything was binding.)

If the car was on the ground, and especially if a wheel suspension member was "hooked" behind the ledge as well, the car might not move at all. In addition, the RR wheel also appears to be right up against the ledge, and this would also prevent any forward motion -- in other words, the wheel would have had to go up before it could go forward. In this case, as the clutch is engaged, the RR wheel would start to spin, the viscous coupler would try to increase torque to the front wheels, but they still couldn't move the car.

After the car was raised a few inches, whatever was catching was free, or less restrained, and the car moved.

A Sub mechanic recently told me "off the record" that a solution to my predicament would have been to open the fuse box under the hood and to put a fuse into the vacant slot marked "FWD" thereby disabling the AWD and turning the car into just FWD.

This applies only to the 4-speed automatic transmission -- not cars with a manual transmission, which is what I believe you have based on your reference to the "clutch". In any event, using the fuse would not be necessary even with the 4-speed automatic.

Given the situation in the photo, I now tend to think it was just well beyond the capability of the car.

[Larry Vollintin]

OK, so a few more facts. No part of the chassis was resting on the ground. The right rear wheel was not hanging freely, but certainly without sufficient weight and contact to get traction. The vertical face of the rock showed I left quite a bit of rubber trying to get out. The front wheels were not on loose gravel and did not spin when trying to engage (and burning up) the clutch. I couldn't rock the car as the rear bumper was pushed up against (but not caught on) even larger rocks in the back. I've attached another photo showing how I got out after sliding the jack under the frame and lifting the entire car enough to push some rocks and large branches under the real right wheel and putting an old blanket over the stuff and the rock. With that help, the car pulled right out with little problem.

So, my question is exactly how does the center differential work on my car and how much torque is shifted to the front wheels or to the LR wheel in such a situation? I didn't get any sense that the front wheels were pulling at all.

As to the FWD fuse "solution", I'll go back to the mechanic about the fuse working only for a 4 speed auto. If I'd had an automatic would it have pulled out on its own? Why? Thanks for the comments. LRV

[subiesailor]

Originally Posted by Larry Vollintin

OK, so a few more facts. No part of the chassis was resting on the ground. The right rear wheel was not hanging freely, but certainly without sufficient weight and contact to get traction. The vertical face of the rock showed I left quite a bit of rubber trying to get out. The front wheels were not on loose gravel and did not spin when trying to engage (and burning up) the clutch. I couldn't rock the car as the rear bumper was pushed up against (but not caught on) even larger rocks in the back. I've attached another photo showing how I got out after sliding the jack under the frame and lifting the entire car enough to push some rocks and large branches under the real right wheel and putting an old blanket over the stuff and the rock. With that help, the car pulled right out with little problem.

So, my question is exactly how does the center differential work on my car and how much torque is shifted to the front wheels or to the LR wheel in such a situation? I didn't get any sense that the front wheels were pulling at all.

As to the FWD fuse "solution", I'll go back to the mechanic about the fuse working only for a 4 speed auto. If I'd had an automatic would it have pulled out on its own? Why? Thanks for the comments. LRV
Attachment 24731

AT would have been better MT the gearing is way to high to tackle this type of technical surface. You couldn't spin the front wheels because you couldn't get enough power to them with the MT ie your gearing was too high and you had to slip the clutch to keep from stalling the car. MT the AWD system is very basic there really isn't anything to fail other than the viscus coupler but that won't matter in this case given you couldn't get enough power to the wheels to start with due to the MT and slipping the clutch.

Not to mention if the rear wheel was spinning enough to put some rubber on the rock - the viscus coupler was working given thats what sends power to the rear of the car. Again your issue would be lack of low gearing in the MT which is why the hard core off road guys in the outback prefer the AT the torque Converter makes up quite a bit for not having low gearing.

The only other possibility is a CV joint which has failed on the front end as a result the axle is turning but the front wheels are not. I highly doubt this though.

[grossgary]

too much for it to pull over, but like was said it is surprising the wheels didn't move.

the rear viscous type LSD's degrade as an open rear differential with age fairly often. so that both rear wasn't spinning doesn't surprise me. the fronts though that is strange.